fix(extension-health): unregister signal listener to avoid potential …

…memory leak

(node:93642) MaxListenersExceededWarning: Possible EventEmitter memory
leak detected. 11 SIGTERM listeners added to [process]. Use emitter.setMaxListeners()
to increase limit

Signed-off-by: Raymond Feng <enjoyjava@gmail.com>

extensions/health/src/__tests__/acceptance/health.acceptance.ts

@@ -7,6 +7,7 @@ import {RestApplication, RestServerConfig} from '@loopback/rest';
 import {
   Client,
   createRestAppClient,
+  expect,
   givenHttpServerConfig,
 } from '@loopback/testlab';
 import {HealthComponent} from '../..';
@@ -41,6 +42,17 @@ describe('Health (acceptance)', () => {
     it('exposes health at "/live/"', async () => {
       await request.get('/live').expect(200, {status: 'UP', checks: []});
     });
+
+    it('removes listener from the process', async () => {
+      const healthChecker = await app.get(HealthBindings.HEALTH_CHECKER);
+      // eslint-disable-next-line @typescript-eslint/no-explicit-any
+      const onShutdownRequest = (healthChecker as any).onShutdownRequest;
+      let listeners = process.listeners('SIGTERM');
+      expect(listeners).to.containEql(onShutdownRequest);
+      await app.stop();
+      listeners = process.listeners('SIGTERM');
+      expect(listeners).to.not.containEql(onShutdownRequest);
+    });
   });
 
   context('with discovered live/ready checks', () => {

extensions/health/src/observers/health.observer.ts

@@ -23,6 +23,7 @@ import {LiveCheck, ReadyCheck} from '../types';
 export class HealthObserver implements LifeCycleObserver {
   private eventEmitter = new EventEmitter();
   private startupCheck: Promise<void>;
+  private shutdownCheck: ShutdownCheck;
 
   constructor(
     @inject(HealthBindings.HEALTH_CHECKER) private healthChecker: HealthChecker,
@@ -37,15 +38,13 @@ export class HealthObserver implements LifeCycleObserver {
       void
     >;
     const startupCheck = new StartupCheck('startup', () => startup);
-
-    const shutdown = once(this.eventEmitter, 'shutdown');
-    const shutdownCheck = new ShutdownCheck('shutdown', () => shutdown);
-
     this.startupCheck = this.healthChecker.registerStartupCheck(startupCheck);
-    this.healthChecker.registerShutdownCheck(shutdownCheck);
+    const shutdown = once(this.eventEmitter, 'shutdown');
+    this.shutdownCheck = new ShutdownCheck('shutdown', () => shutdown);
   }
 
   async start() {
+    this.healthChecker.registerShutdownCheck(this.shutdownCheck);
     const liveChecks = await this.liveChecks.values();
     const liveCheckBindings = this.liveChecks.bindings;
     let index = 0;
@@ -72,6 +71,14 @@ export class HealthObserver implements LifeCycleObserver {
 
   stop() {
     this.eventEmitter.emit('shutdown');
+    // Fix a potential memory leak caused by
+    // https://github.com/CloudNativeJS/cloud-health/blob/2.1.2/src/healthcheck/HealthChecker.ts#L118
+    // eslint-disable-next-line @typescript-eslint/no-explicit-any
+    const onShutdownRequest = (this.healthChecker as any).onShutdownRequest;
+    if (onShutdownRequest != null) {
+      // Remove the listener from the current process
+      process.removeListener('SIGTERM', onShutdownRequest);
+    }
   }
 }